Producing sound records in half-wave records



Feb. 22, 1944. c. BECKER 2,342,239

PRODUCING SOUND RECORDS IN HALF-WAVE RECORDS Filed Aug. 27'. 1940 2Sheets-Sheet 1 Jnranfar 6. 3e c /(e 7 3y- 4w,

Feb. 22, 1944. c. BECKER 2,342,239

PRODUCING SOUND RECORDS IN HALF-WAVE RECORDS Fi led Aug. 27, 1940 I 2Sheets-Sheet 2 J/Wen/or:

mama m. a, i944 PRODUCING SOUND RECORDS IN HALF-WAVE RECORDS CarlheinzBecker, Berlln-WilmersdorLGermany; vested in the AlienPropcrtyflnstodian Application August 27, 1940, Serial No. 354,459 InGermany March 18, 1939 lclaim.

The present invention relates to sound recording and, particularly, tothe making of half-wave records which are referred to as push-pull classB records.

An object of the invention is to avoid disturbances and distortionswhich previously occurred when the alternating current is divided intotwo half waves.

Other objects and advantages will be apparent from the followingdescription of detailed embodiments of the invention, when read inconnection with the accompanying drawings, inwhich:

Fig. 1 shows a circuit for producing half-wave records, and Figs. 2 to 6show different embodiments of the invention wherein the disturbances anddistortions are avoided.

Referring to the left-hand side of Fig. 1, ,tli'e previously amplifiedmicrophone voltage is applied their respective windings.

across a resistance unit- I which is connected between the cathode andgrid of an amplifier tube 2. The cathodeanode-circuit of tube 2 isformed by a battery 3 and the primary winding 4 of a push-pulltransformer having two secondary windings 5 and 8. Winding 5 isconnected across a resistance 9 with one side being connected through adiode I; similarly, winding 8 is connected through a diode 8 across aresistance It.

The diodes allow currents to pass in one direction only with the resultthat, during one half of each cycle, current flows from winding 5through diode 1 and resistance 9; and, during the other half of eachcycle, current flows from winding 8 through diodB 8 and resistance III.This produces onehalf wave voltages across resistances 9 and In whichare supplied to the recording mechanism.

It has been found that this arrangement for producing sound recordingsin half-wave records has the following disadvantages:

At each reversal of the current flow through the I transformer, thediodes I and 8 operate in such a manner that one of the push-pullcircuits is cut in and the other is cut out. Due to the fact thatsubstantial power is required for operating the recording mechanism,considerable current flows with the result that the effect oi cutting inand cutting'out the circuits is appreciable. In each of windings I andI. the self-induction tends to cause disturbances in the push-pullcircuit itself as well as through a reactive effect in the other isprovided for a circuit such as that shown in Fig. 1 Here, thetransformer is designated at 3; Each push-pull circuit is provided witha second parallel circuit, there being a circuit formed by diode 'l' anda resistance 9' connected in parallel with the circuit, of resistance 9and diode 1 and there being similarly a circuit formed by a diode 8' anda resistance [0' which is connected in parallel/with the circuit ofresistance 10 and resistances lfl and ID are similarly related. Duringoperation, the auxiliary parallel circuits formed by diodes Iandiresistance 9' and diode 8' and resistance l0 respectively drawcurrent from In the embodiment of Fig. 3, the two push-pull circuits aresupplied through separate transform- .ers'3 and 3', respectively,transformer 3' having a primary winding 4'. Primary winding 4 receivescurrent through tube 2 and primary winding 4' receives current through asimilar tube 2. By

this arrangement, the change of 'current in one of the secondarywindings does not eiiect the other transformer. In this way,.the majorsource of the distortion is eliminated.

The further modification of Fig. 4 avoids the disturbances bythe'connection of the diode circuits. As indicated above in connectionwith the discussion of Fig. l. the disturbances and distortions dependin part on the intensity of the current flowing in the push-pullcircuits and it is desirable to. maintain these currents as small aspossible. However, due to the fact that considerable power is requiredto operate the recording push-pull circuit. These various disturbancesof the mechanisms which are connected to resistances l and II, it isdesirable that these currents be large and in the embodiment of Fig. 4very high ohmic values are chosen for resistances 8 and II with theresult that small currents flow through these resistances and nosubstantialdis tortion o'r disturbance results. Resistance 9 isconnected across the cathode-grid circuit of an amplifier tube ll,the-cathode-anode circuit of which is connected to a battery across aresistance I 3; similarly, resistance I0 is connected across the cathodegrid circuit of an amplifier tube I! which has its cathode-anode circuitconnected through the battery across resistance It. Changes in voltageacross each of the resistances 0 and I0 cause corresponding changes inthe voltage across the respective resistances I! or H, and s uiiicientpower is available from the circuits of hettery.

This defect is arm in occordance with the present invention by insertingin each or the diode circuits an adjustable negutivecountervoltege-which is of such e value that theefi'ective operatingcharacteristics of the, diode pess through the zero point.

Referring to Fig. 5, the common line between the, push-=pull circuits isprovided with a. counter voltage unit. unit is formed by potentiometer655 which hes connected across its ends.

e. hotter it. By adjusting the contact on the notentiometer, the propervoltage is placed in series in the diode circuit so thet the effectiveoperating characteristics of the diodes i and 8 pass through zero. Inthis way, the diodes eliow a flow of current in one direction only.

In making records, it is necessary to supervise the half-wave voltageswhich ere impressed upon the recording device. In the illustrativeembodiment of the invention represented in Fig. 6, the two half wavesare composed intoe complete curve again and the resultant voltage issupplied by way of an amplifier to a control memloer such as a Breuntribe or a. loud speaker. 'Ihis composition is eil'ected in a simplemanner by providing'o. circuit such as described above and the includ ngin each of the push-pull circuits 8. takeofl circuit parallel to theoutput from which the either at resistances 9 It or at resistances l1and it. Volteges for control v w are taken on through condensers 22 andare impressed upon the grids of tubes l9 and so which are arranged inpush-pull fashion. The two enodes oi tubes 89 and it are connec to theopposite ends of the primary windings of transformer 2i. and the centertop is connected to one side of the other side of the battery isconnected to the cathodes oi the two tuhes end else to the we line ofthe resistances 9 end it.

- to the grids of tuhes it] end it; form a complete half-wave isimpressed upon an amplifier circuit.

Referring particularly to Fig. 6, the recording members are suppliedwith half-wave voltoges The secondary i 11-: of transformer H isconnected to the control memher. El g operetion, the half-wove voltageswhich occur at resiston c m it end 08 are displaced 180." and thehalf-wove voltcges occng ot the resistances 9 end [it] respechvely, endthe voltages applied were. Condensers 22 ere ler in theircherecteristics so that voltages of equol magnitude are topped fromresistances it and as and re sistences 9 and G6,.

What 1 clnim is:

In a push-pull amplifying circuit of the type including a. transformerhaving its primary connected to a, source of speech currents and itsdivided secondary applied w wetricelly in push pull coupling to e pairof rectifier tub-es and loeding resistors in series connectiontherewith, whereby a halt-wove signal oppeers across one of the loadingresistors and the. corresponding half-wove signal of opposite polarityeppeers across the other loading resistor, means for reducing distortionduring amplification said means comprising a. shunt circuit consistingof a. rectifier and e. loading resistor connected across each half ofthe divided secondary, whereby currents of opposite polarity to thehalf-wave signal are dissipated in the resistor which forms a, port ofthe shunt circuit.

CZ BECKER.

